1. Field of the Invention
This invention relates to motor actuator circuits, and more particularly, to an integral motor controller circuit which controls motor speed and the direction of rotation of the motor shaft as a function of changes in a sensed parameter.
2. Description of the Prior Art
Motor control circuits are employed in analog control systems for controlling a motor which controls system apparatus to maintain a variable system parameter at a predetermined set point value. The motor controller circuit is responsive to an input signal representing deviations of the parameter from the set point to supply drive signals to the motor. The motor in turn controls apparatus of the system to correct for the error.
One example of the use of a motor controller circuit is in an environmental control system wherein a reversible motor drives a damper actuator which controls dampers located in air ducts supplying warm and cool air to an area or room to position the dampers as a function of the temperature in the area as sensed by a temperature sensor. The motor effects repositioning of the dampers to permit warm or cool air to be supplied to the area as needed to compensate for the change in temperature.
In known systems, the motor controller circuit supplies a fixed drive to the motor such that is driven at a constant speed which enables effective compensation for average deviations from the set point. However, the correction may be too fast for small deviations and too slow for large deviations. Thus, in the case of large deviations, for example, it may take a long time to return the air temperature in the area to the desired temperature set point. This is undesirable in heating and air conditioning systems where the temperature should be maintained at the set point value, and in the event of a sudden change in load requirements, that a demand for heating or cooling, the temperature should be returned to the set point as quickly as possible to maintain comfort for occupants of the area.
Also, in such systems, a reversible motor is generally required to permit opening and closing of a damper. Thus, the motor controller circuit must provide bi-directional drive to the motor to compensate for positive or negative deviations from the set point.
Therefore, it would be desirable to have a motor controller circuit which provides bi-directional drive to a motor and in which the speed of correction is a function of the amount of deviation from the set point.